Hello. Today, my biology professor was late to class and later went on to explain that she had a weird infestation of flies in her apartment. She began by saying that she always leaves her balcony door open, but only a few inches so that her cats may go in and out. She turns all the lights off when she leaves, so as not to attract a load of insects. The poor woman got home very late last night and when she opened her bathroom door, she found hundreds of these giant flies in there. She said they must've been a half-inch long, and that they were normal flies, but very fast. She had them all over her house, but she also mentioned that there was a decaying mole in her file cabinet which she found the day before. Her cats bring all sorts of dead stuff into her house, but she has never had the misfortune of a random explosion of flies. She said that there were no flies in her house the day before, and that the mole had been in the house long enough to where it let out a fume which she used to find it. The class discussed the problem, and I concluded that the flies were already in her house, because there were no other kinds of insects there before, and no lights on. If it was because of light, she should've had dozens of kinds of insects, not just one kind of fly. Ultimately that's where the discussion ended. No one could think of how the flies got in her house, other than them coming from the dead mole. I feel so bad for her. She's the best professor I've had, and just about every one of her students in this class is trying to research on how this could've happened. I'd appreciate it if you guys could help me in figuring out how hundreds of flies suddenly showed up. Thank you!

I would agree that it was probably flies from maggots, and it's also possible that she didn't find the WHOLE mole, or there may have been more than one - it's possible that in or near a bathroom, the odor might have been minimized or less noticeable.

If the flies were hatchlings then they would all be small but the ones that appear suddenly are large black flies. I have had the same experience with this 'sudden fly invasion' in Sebastopol, California. There are two residences on the property and this has happened in both houses. The second time was much worse than the first time. I would guess the first appearance of flies to be in the 100's but this last time would be in the thousands. The room they were in was completely sealed from the outside. There was nothing dead in the room so we need an explanation for what is happening here.Thanks.S